1. Field of the Invention
The present invention relates to a noncontact power transmission system that contactlessly transmits electric power from a power transmitting device on the primary side to a power receiving device on the secondary side using electromagnetic induction.
2. Description of the Related Art
A noncontact power transmission system of this type has conventionally been disclosed in, e.g., JP-A-2006-60909 (hereinafter referred as Patent Document 1).
The noncontact power transmission system described in Patent Document 1 verifies whether or not a power transmitting device and a power receiving device are regular, by means of mutual communication, prior to power transmission and, until completion of the verification, the power transmitting device does not start full-scale power transmission to the power receiving device.
In addition, another conventional noncontact power transmission system, for example, that performs such an operation as illustrated in FIG. 6 has been known.
As illustrated in FIG. 6, the power transmitting device side intermittently supplies electric power to a self primary coil during a predetermined time T1 and performs an operation corresponding to the presence/absence of a response from the power receiving device side. In other words, the power transmitting device stops power supply to the primary coil unless there is a request for authentication from the power receiving device side after lapse of the predetermined time T1. On the other hand, the power transmitting device performs an authentication operation if there is a request for authentication from the power receiving device side after lapse of the predetermined time T1 and, when the authentication is satisfied, starts a power transmitting operation to the power receiving device.
Referring next to a flowchart in FIG. 7, detailed description will be made on operations thereof.
The power transmitting device side starts drive of the primary coil (step S1), then performs detection of the authentication (step S2) and, if the detection fails, stops driving the primary coil (step S3). On the other hand, as described later, when the detection is succeeded, a predetermined authentication operation is performed (step S4).
The power receiving device side, when the self secondary coil and the primary coil of the power transmitting device are electromagnetically coupled together, receives electric power high enough to start (step S5). The receipt of power causes power-on reset (step S6) and the power receiving device starts an authentication operation between the power transmitting device and itself (step S7).
Upon the authentication operation, the power transmitting device side can detect the authentication, and thus performs a predetermined authentication operation (step S4). If it is determined by the authentication operation that power transmission to the power receiving device is allowed, the power transmitting device starts transmission of electric power to the power receiving device.
In a conventional noncontact power transmission system that performs such an operation as illustrated in FIGS. 6 and 7, the power transmitting device side needs to detect a request from the power receiving device side when intermittently supplying power to a self primary coil only during the predetermined time T1.
Accordingly, the power transmitting device needs to supply power to the primary coil during the predetermined time T1 until the power receiving device is ready to respond, and there is a problem of power consumption that increases on standby as the predetermined time T1 increases, which requires a solution thereto.
In view of the foregoing problems, it is an object of the present invention to provide a noncontact power transmission system that can reduce power consumption of a power transmitting device on standby by reducing time of feeding a primary coil in intermittently operating the power transmitting device.